Forward DC-DC ZVS converter and control scheme

Abstract

The proposed solution allows a forward DC-DC converter's isolated transformer to resonant reset and the forward DC-DC converter to operate in ZVS condition regardless of whether the output inductor current is in DCM or CCM. To compare with a regular forward DC-DC converter, the output isolated transformer has an extra reset winding Nt in addition to the regular primary and secondary windings Np and Ns. Based on the rule of the magnetic flux remaining unchanged for the forward output isolated transformer, it is the extra reset winding Nt, a resonant capacitor Cr, an additional MOS Q 2 and the related control function block M that allow the forward output isolated transformer to finish resonant reset and the primary main power MOS Q 1 to operate in ZVS. The magnetizing current of the forward output isolated transformer is fully utilized, and regardless of whether the resonant reset circuit is on the primary or the secondary, the magnetizing current can enable the forward output isolated transformer to resonant reset and serve as the main power MOS Q 1 operation in ZVS.

What is claimed is: 
     
       1. A forward DC-DC ZVS converter comprising:
 a function block, an output isolated transformer, and a related forward DC-DC converter; 
 wherein the output isolated transformer comprises a primary winding, a secondary winding, and a reset winding in tight couple through a magnetizing core; and the output isolated transformer comprises a magnetizing inductor; wherein the inductance value of the related magnetizing inductor is changed with turns-ratio square of the output isolated transformer; and two terminals of the secondary winding Ns are connected with the cathodes of the output diode D 1  and the freewheel diode D 2  separately; and the anodes of the output diode and the freewheel diode are connected together with negative terminals of an output filter capacitor Cf and the load; and the cathode of the freewheel diode is connected with one terminal of an output inductor, and the other terminal of the output inductor is connected with the positive terminals of output filter capacitor and the load; 
 wherein a first pin of the function block M is connected with a gate of a primary MOSFET; and a second pin of the function block M is connected with a gate of a second MOSFET; and a third pin of the function block M is connected with a source of the second MOSFET and ground; and a source of the primary MOSFET is connected through the sense resistor into ground; and the reset winding Nt and a resonant capacitor with a parallel diode are connected with the related pins of the function block; 
 wherein the function block comprises two parts, one part of the divided function block is configured to control the on or off of the primary MOSFET turn; and the other part of the divided function block is configured to control the on or off of the second MOSFET; and based on the current of the reset winding or the voltage of the resonant capacitor, feedback signal, the function block M is configured to control the resonant reset through control the on or off of the resonant reset second MOSFET; 
 wherein V IN  is a primary side input DC voltage; and V IN  is connected with the homonymous end primary winding of the output isolated transformer; and the non-homonymous end primary winding of the output isolated transformer is connected with the drain of the first MOSFET. 
 
     
     
       2. The forward DC-DC ZVS converter of  claim 1 , wherein the function block, there are a resettable integrator, comparator+limited amplitude error amplifier, cross zero+delay module; and the source of the second MOSFET is connected to ground through the sense resistor Rc; and the homonymous end reset winding of the output isolated transformer is connected with the drain of second MOSFET and the non-homonymous end reset winding of the output isolated transformer is connected to ground through the resonant capacitor; and the diode is parallel with the resonant capacitor, and the anode of the diode is connected with ground; and the output of the comparator+limited amplitude error amplifier module is connected with the gate of the second MOSFET; and the sense voltage on the sense resistor Rc is used as an input signal for the resettable integrator and the comparator+limited amplitude error amplifier module; and the output of the resettable integrator is as an input for the comparator+limited amplitude error amplifier module and the cross zero+delay module; and the output of the cross zero+delay module is another input of the comparator+limited error amplifier module. 
     
     
       3. The forward DC-DC ZVS converter of  claim 1 , wherein the function block is composed of compare+limited amplitude error amplifier and zero cross+delay module; and the source of the second MOSFET is in ground; and the drain of the second MOSFET is connected with the homonymous end reset winding of the output isolated transformer; and the non-homonymous end reset winding of the output isolated transformer is connected to ground through the resonant capacitor; and the diode is parallel with the resonant capacitor; and the anode of the parallel diode is in ground; and the output of compare+limited amplitude error amplifier is connected with the gate of the second MOSFET; and the voltage on the resonant capacitor is output through voltage divider network; and the voltage divider is composed of Ru and Rd; and the output of the voltage divider is as an input signal for compare+limited amplitude error amplifier and zero cross+delay module; and the output of zero cross+delay module is another input for the compare+limited amplitude error amplifier. 
     
     
       4. The forward DC-DC ZVS converter of  claim 1 , wherein the resonant reset with the reset winding can be in the primary side of the output isolated transformer to make the primary MOSFET turn-on in ZVS; and the resonant reset with the reset winding also can be in the secondary side of the output isolated transformer to make the primary MOSFET turn-on in ZVS with an additional function block M 1 . 
     
     
       5. The forward DC-DC ZVS converter of  claim 1 , wherein the reset winding and the second MOSFET are used to finish the resonant reset for the output isolated transformer and make the primary MOSFET turn-on in ZVS to decrease the switching loss; and based on the current or voltage of the resonant reset, the function block controls the on or off of the second MOSFET to make the output isolated transformer resonant reset and the primary MOSFET turn-on in ZVS to down switching loss; and as the second MOSFET turns on, the resonant capacitor is reflected into the primary winding of the output isolated transformer through the reset winding and resonated with the magnetizing inductor Lm of the primary winding; and as the resonant reset is finished, the current in the reset winding reaches reverse peak of magnetizing current; and as the function block controls the second MOSFET turn-off, the reverse magnetizing current in the reset winding is automatically transferred into the primary winding; and as long as the reverse magnetizing current is high enough, the reverse magnetizing current can discharge the drain capacitance voltage of the primary MOSFET from the input voltage V IN  to zero and make the body diode of the primary MOSFET turn on to feedback the magnetizing energy into the input DC voltage V IN ; and at this moment, the function block controls the primary MOSFET turn-on; and due to the body diode of the primary MOSFET turn-on, the primary MOSFET is turned on in ZVS condition with lower switching loss.